The attack on the dam was the latest reminder of militants' intent to undermine major infrastructure projects in Iraq, and highlighted continued instability in northern Nineveh province. U.S. military officials acknowledge that insurgents have sought shelter in the north after being driven out of Baghdad and other provinces by major summer military offensives.

The bombed bridge connects the right and left shores of the Mosul dam and had been used by vehicles for the last three decades.

Reconstruction work on the Mosul dam, which was built during the 1980s, has been one of the major projects undertaken with the nearly $20 billion in funds that Congress approved for Iraqi reconstruction in 2003. The money was a one-time allotment, and only about $2 billion is left, making extra costs caused by security breaches especially troublesome, said a U.S. official involved in Iraqi reconstruction work.

Repairs are needed on the dam to keep water at a safe level behind the reservoir, the official said.

U.S. engineers have expressed concern about the dam bursting, causing massive flooding as far away as Baghdad, approximately 250 miles south.

Syrian trucks coming from the northern Iraqi border use the bridge to transport gasoline and other goods, locals said. U.S. forces and Iraqi security forces also use the bridge.

Elsewhere in Iraq, government officials and security forces said the transfer of control of Iraq's southern Babil province from U.S. forces to Iraqi authorities would be delayed indefinitely.

"No time and place have been decided yet," Brig. Gen. Faris Jibouri, acting police chief in the provincial capital of Hillah, told the Los Angeles Times.

In November, a provincial government spokesman and a police spokesman told reporters in Hillah that Dec. 17 or 18 were possible dates for the hand-over. And on Monday, a member of Babil's provincial council said Dec. 16 also had been considered as a possible transfer date.

But U.S. military officials in Baghdad said Monday that Babil is not scheduled "for provincial Iraqi control until June 2008," and only the transfer of Basra province, in the country's south, had been set for December.